Waste management still remains a challenge to the urban, semi-urban, rural, developed, developing and under-developed communities and civilizations and lack of necessary knowledge and resources is further hampering intentions and initiative for the same. Ozone depletion, exponentially rising values of per capita carbon foot-prints, greenhouse emissions and global warming are subjects of discussion, debates and negotiations globally, compelling researchers to seek short term as well as long term solutions for reversing the negative trends. As a result, an immense amount of research is being poured into achieving ways and means for waste management while utilizing humongous amounts of wastes generated as sources for generating forms of renewable energy.
Various methods of waste management such as land filling, plasma arc waste disposal, gasification, trans-esterification, incineration, bio-drying, mechanical heating, pulverising and thereafter pelletizing, combustion of dry waste material, fermentation into bio-gas making, etc. have been researched upon and are now being looked into for development of resources for sustainable and renewable sources of energy. Most of these processes involve extraction of hydrocarbons using any suitable process and their subsequent cracking. Processes for different types of cracking of hydrocarbons are known such as thermal cracking, pyrolytic cracking, etc. and are employed with or without use of catalysts. The cracking processes using catalysts may employ homogenous or heterogeneous, fixed-bed or fluid-bed catalysts.
Conventionally, some processes utilise catalysts by mixing them intrinsically with reactants. Such a step does not guarantee a uniform contact between the catalyst and reactants; as a result, the catalytic conversion/reaction is rendered inefficient and incomplete generating waxy and inconsistent products. When catalysts are mixed along with the feed material at fixed weight proportions, the volatile gases generated often lead to catastrophic explosions. Further, the end products like the liquid fuels, the non-condensable gases in such processes end up laced with the catalyst residues which contaminate the quality of the yield. The discharges from the process also contain the residual catalyst material, which makes the discharges an environmental hazard. Such discharges are inappropriate and unfit to be land-filled or disposed off in any other manner.
External catalysts may be used, but they have a limited tolerance for moisture in the reactants and/or vapour feed, being catalysed. The catalysts get eroded or contaminated over a short period of time while being utilised in the process. The time and effort required to replace the catalysts add substantially to the operational down time and subsequently, operational costs of the plant. Conventional catalysts used in multitude of processes lead to various effluents in each of the varied processes. Besides, the vapours and reformed gases from the catalytic convertors often require secondary processing to remove particulate matter using hydro cyclones from gases and filters to clean liquid fuels. This adds to increased capital and operational costs, larger equipment foot print and frequent maintenance. The presence of pollutants in the gases, require an additional step of scrubbing. Scrubbers which conventionally use liquid phase scrubbing agents, lead to increased capital costs, operational costs besides adding to the disposal problems with scrubbing fluids.
WO 2005/087897 describes a process and plant for thermo catalytic conversion of waste materials into reusable fuels and a fuel produced by the said process. The application proposes use of a conventional catalytic reactor tower that uses high surface area metal plates arranged in a torturous path as catalysts. The said arrangement thus becomes bulky and inconvenient for serviceability and maintenance and requires a halt in the working of the plant in order to carry out the servicing and maintenance. The functioning of the said tower is dependent upon maintaining its temperature to 220° C. thus adding to the additional steps and operational parameters required in the process. Besides, the non-condensable gases and the liquid fuels require additional filtration and scrubbing steps which add to additional equipment, increased capital cost and many more equipment requiring maintenance in the operation of the plants.
Thus, there is need in the present state of the art for a stable catalytic conversion system that is hassle free, convenient, durable, and recyclable and incurs least maintenance and operation costs.